Sure. Name a war that the US was a party in which signals intelligence did not play a signifigant role.
Remember Pearl Harbor? Hours before the attack the Signals Intelligence Service - a preciursor of the National Security Agency - intercepted the diplomatic message from Tokyo to the Japanese ambassodor to the US in which Japan informs the US of attacks and breaks off diplomatics relations.
In the US Civil War, there was a almost universal practice of telegraph taps to glean intelligence from opposing forces. In fact, modern US cryptographic practices date back to the US Civil War.
There was a incident during WWII, related in his six-volume history, where Britsh PM Winston Churchill had his private phone call to FDR interrupted by a US telephone censor for discussing strategic matters over an unsecure line.
During the course of the war, civilian communication from sensitive war industry areas such as Oak Ridge, Los Alamos, and naval yards were routinely monitored for espionage indicators.
Once again quoting Justice O'Connor in
Hamdi:
In light of these principles, it is of no moment that the AUMF does not use specific language of detention. Because detention to prevent a combatant’s return to the battlefield is a fundamental incident of waging war, in permitting the use of “necessary and appropriate force,” Congress has clearly and unmistakably authorized detention in the narrow circumstances considered here.